This invention relates to a metal strip casting apparatus in which molten metal is brought into contact with a casting roll surface so as to solidify on that surface. More specifically, it is concerned with cleaning of the casting rolls in such casters.
The casting apparatus may be either a single roll caster or a twin roll caster. In a twin roll caster hot metal is introduced between a pair of contra-rotated horizontal casting rolls which are cooled so that metal shells solidify on the moving roll surfaces and are brought together at the nip between them to produce a solidified strip product at the outlet from the roll nip. The term “nip” is used herein to refer to the general region at which the rolls are closest together. The hot metal may be introduced into the nip between the rolls via a metal delivery nozzle located above the nip to form a casting pool supported on the casting roll surfaces immediately above the nip and confined at the ends of the nip by appropriate confining means such as pool side damming plates.
In order to prevent accumulation of metal oxides and slags or other contaminants on the roll surfaces, cleaning devices such as brushes or cleaning belts may be applied to the outer longitudinal surfaces of the rolls so that the roll surfaces are continuously cleaned before moving into contact with the molten metal in advance of the nip. One apparatus of this kind is disclosed in Japanese Patent Publication JO3230849-A of Nippon Steel Corporation and Mitsubishi Heavy Industries KK. In this apparatus two sets of divided roller brushes are applied to the peripheral surface of each chilled casting roll with the brushes of one set being staggered with respect to those of the other set to provide a brushing action across the complete width of the casting roll. Japanese Patent Publication J01-083341-A also of Nippon Steel Corporation and Mitsubishi Heavy Industries KK also discloses a twin roll caster in which the casting rolls are cleaned by brushes. Japanese Patent Application 29393/97 and 29394/97 of Nippon Steel Corporation disclose roll cleaning arrangements in which two cylindrical cleaning brushes are brought successively into contact with a casting roll at different stages of a casting run. U.S. Pat. No. 4,793,400 discloses a casting drum cleaner in which a pair of similar rotating brushes are applied in tandem to the drum, both brushes being driven in opposite directions to the rotation of the drum. Other roll brushing arrangements are disclosed in our U.S. Pat. Nos. 5,307,861 and 5,575,327.
It has been found that during the start and finish of a casting operation, the casting roll picks up major accretions of contaminants and these can damage the brushing device which must be capable of performing fine cleaning of the casting surface during normal casting. The contaminants can also damage the casting roll surface if they accumulate between the casting rolls and the metal delivery support plate. The present invention provides a brushing device by which a rotary sweeper brush can be brought into engagement with the casting roll surface in advance of a main brush to sweep off such major accretions at least during the start and finish of a casting run.